I think Tremor is high mid tier at worst and top 10 at best. Despite all the negative changes to armor moves, up rock, and the EX ground pulse OTG, he has somehow managed to remain a viable and strong character.
1. Crystalline is the best variation because of its offensive options.
2. Aftershock is the close second best while Metallic is the distant third best variation.
3. I think any character who zones and controls the air efficiently will give Tremor a difficult time.
4. Tremor will do well against any character who does not fit the description above.